Pulverizer tyre

Abstract: Reinforcing sections (36,38) are provided at an outer surface (34) and at an inner surface (32) of a tyre (20) for a roll wheel assembly used in a pulverizer for crushing a material such as coal. These reinforcing sections (36,38) cause the tyre to be asymmetrical and are located on the tyre only at areas where the wearing of the tyre is highly predictable. The reinforcing section (38) provided on the inner surface (32) of the tyre (20) is provided directly opposite the reinforcing section (36) on the outer surface for preventing the localized thinning of the tyre and extending the time interval between rotation and/or replacement of the tyre.

Description: The present invention relates to tyres used in a roll wheel assembly in a pulverizer for crushing material such as coal. Pulverizers are commonly used to grind various materials in the coal processing, ceramic, and chemical industries. A roll and race pulverizer uses grinding elements comprising a plurality of roll wheel assemblies or tyres suspended from driving arms and which rotate around their respective axes of rotation through contact against a grinding ring or race for grinding and reducing the size of the incoming material, particularly coal. Each grinding element or roll wheel assembly uses a replaceable outer tyre. Currently, the replaceable outer tyres used in the roll wheel assemblies are manufactured from alloy as a casting and are symmetrical about a radial centre plane. Despite the symmetrical orientation of the replaceable outer tyres of the roll wheel assemblies, the tyres wear unevenly during normal pulverizer operation. The problem with uneven wear can be resolved by assembly rotation; i.e., a side-to-side reversal of the partly worn tyre comprising each roll wheel assembly. However, to perform this operation the pulverizer has to be stopped and taken out of service for a significant period of time. The task of pulverizer tyre rotation requires removal of the entire roll wheel assembly from the pulverizer through an access door. This is a difficult and labour intensive operation; special equipment is required because each roll assembly can weigh as much as 35,000 pounds (16,000 kg). Once removed from the pulverizer, the tyres must be disassembled from the roll wheel assemblies by performing a heating operation. This raises the possibility of local overheating and resultant cracking, which will require the tyre to be repaired, if possible, or replaced. Additionally, only a slight improvement in useful tyre life is achieved through this tyre rotation procedure, and it is generally not enough to justify the costs involved. Thus a need exists for an improved pulverizer tyre for a roll wheel assembly that can provide increased wear life at minimal additional cost. European Patent Application No. EP-A-0 110 191 discloses a trimetal pulverizer roll for use in a bowl mill. The core material of the trimetal roll is a relatively soft material having good machinability. An intermediate layer is fabricated from a material having medium wear resistance. The outer layer of the roll is made of a material having highly abrasive resistant qualities. According to one aspect of the invention there is provided a tyre for a roll wheel assembly used to crush material in a pulverizer, the tyre having an asymmetrical outside diameter outer surface for contacting and crushing the material, the tyre comprising: a first reinforcing section on the outer surface of the tyre providing the asymmetrical outside diameter outer surface at a location where the tyre is subjected to wearing due to performing the crushing of the material; and a second reinforcing section on an inner surface of the tyre directly opposite the location where the tyre is subjected to wearing for minimizing localized thinning of the tyre. According to another aspect of the invention there is provided a method of prolonging the use of a tyre of a roll wheel assembly for a pulverizer used for contacting and crushing a material, the method comprising: providing a reinforcing section on an outer surface of the tyre to provide an asymmetrical outside diameter outer surface on the tyre at a location where the tyre is subjected to wearing due to performing the crushing of the material; and providing a reinforcing section on an inner surface of the tyre directly opposite the location where the tyre is subjected to wearing for minimizing localized thinning of the tyre. A preferred embodiment of the present invention provides a replaceable outer tyre for a roll wheel assembly having a reinforcing section at the outer surface of the tyre for contacting and crushing the material. A second reinforcing section is provided on an inner surface of the tyre directly opposite the reinforcing section on the outer surface of the tyre for minimizing wearing of the tyre. The reinforcing sections can be made of a reinforcing material which is located at the outer surface and the inner surface of the tyre where the tyre is most likely subjected to normal wear. The reinforcing sections minimize localized thin spots which can occur during normal wear of the tyre. The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: Figure 1 is a perspective view of a pulverizer; Figure 2 is a cross-sectional view of a roll wheel assembly of the pulverizer of Figure 1; Figure 3 is a schematic representation of the grinding element profiles of a tyre for the roll wheel assembly of Figure 2 showing how they wear from initial profile to end of useful life; Figure 4 is an elevational side view of a tyre according to an embodiment of the present invention; and Figure 5 is a cross-sectional view taken along a line 5-5 of the tyre of Figure 4. Referring to the drawings generally, wherein like numerals designate the same elements throughout the several drawings, Figure 1 shows a perspective view of a pulverizer 10 for grinding incoming material such as coal. The grinding or crushing of coal in the pulverizer 10 is conducted within a pulverizer housing 12. The pulverizer housing 12 contains a plurality of roll wheel assemblies 14, typically three in number, which are pressed against a grinding ring 16 by a spring loading system 18. The grinding ring 16 rotates about a vertical axis of the pulverizer 10, and each of the plurality of roll wheel assemblies 14 has a replaceable outer grinding element or tyre 20 mounted for rotation thereon. Each tyre 20 rotates around its respective axis of rotation through contact against the grinding ring 16, the incoming material being crushed therebetween. Referring to Figure 2, each roll wheel assembly 14 comprises the replaceable outer grinding element or tyre 20 supported on a tyre support 22 rotatably mounted about an axle 24 of the roll wheel assembly 14. Each roll wheel assembly 14 uses a roll pin block 26 and a roller bracket 28 to allow the tyre 20 to rotate about its axis as the grinding ring 16 rotates within the pulverizer 10. A roll air seal 30 is provided for sealing coal and other abrasive particles out of the roll wheel assembly 14. Figure 3 illustrates the design of tyres 20 commonly used in the pulverizer 10. It will be observed that the tyres 20 commonly used in these pulverizers 10 each have an inner section 32 and a wear zone 34 which contacts the material lying within the grinding ring 16. The tyres are commonly made of a highly abrasion resistant material such as one of the white irons specified in ASTM A 532. During normal use, the tyre 20 is reduced in size because of the abrasive properties of the material being ground, the tyre 20 wearing at the wear zone 34 which results in a thinning of the tyre 20. Referring now to Figures 4 and 5, there is shown an embodiment of the present invention. As shown therein, the embodiment comprises the tyre 20 having a reinforcement section 36 located at the wear zone 34. A reinforcement section 38 is also provided at the inner section 32 of the tyre 20 directly opposite the wear zone 34 for preventing localized thinning of the tyre 20 as it wears during pulverizer operation. The reinforcement sections 36 and 38 are preferably made of the same material or alloy as that of the remainder of the tyre 20, or they can be made of a different wear resistant material to further enhance the wear life of the tyre 20. The reinforcement sections 36 and 38 may be affixed to an existing tyre 20 by means of weld deposition methods, or they can be part of the tyre in an as-cast configuration. Composite casting methods, i.e. wherein preformed reinforcement sections are placed in the casting mould prior to pouring the molten metal forming the balance of the tyre, can also be employed to produce a tyre 20 with the reinforcement sections 36 and 38. Alternatively, the reinforcement sections 36 and 38 can be made as separate elements which are then later mechanically affixed via fasteners or the like to an existing tyre 20. Finally, yet another approach to creating a tyre 20 with the reinforcement sections 36 and 38 is to add them by sleeving them over and into an existing tyre 20. The present technique thus provides for a tyre 20 having an asymmetrical outside diameter surface which results in improved wear life with only a minor increase in maximum section thickness. An immediate benefit is that the time interval between pulverizer tyre 20 rotation and/or replacement is increased. In lieu of the aforementioned asymmetrical outside diameter surface, a larger symmetrical outside diameter surface could be added. However, this would be a costly and inefficient use of costly alloy material. In lieu of an inside surface that approximates the outside wear configuration, a tyre 20 could be designed with a symmetrical inside surface having an equivalent minimum thickness or with a solid alloy core. However, once again this would be a less efficient use of this costly alloy material. In addition, a massive increase in section thickness greatly increases the difficulty of achieving reliably sound castings and attendant increases in reject rates for these castings and associated costs. Reinforcement sections 36 and 38 are provided on the tyre 20 only at predictable high wear areas, resulting in an approximately 30% increase in tyre wear material thickness, with only an approximately 10% increase in overall tyre weight.

Claims: A tyre (20) for a roll wheel assembly (14) used to crush material in a pulverizer (10), the tyre (20) having an asymmetrical outside diameter outer surface for contacting and crushing the material, the tyre (20) comprising: a first reinforcing section (36) on the outer surface of the tyre providing the asymmetrical outside diameter outer surface at a location where the tyre is subjected to wearing due to performing the crushing of the material; and a second reinforcing section (38) on an inner surface (32) of the tyre directly opposite the location where the tyre is subjected to wearing for minimizing localized thinning of the tyre. A tyre (20) according to claim 1, wherein the reinforcing sections (36,38) are at areas where the tyre wearing is predictable. A tyre (20) according to claim 1 or claim 2, wherein the tyre (20) is made of an alloy. A tyre (20) according to claim 3, wherein the reinforcing sections (36,38) are made of the same alloy as the tyre (20). A tyre according to claim 1, claim 2 or claim 3, wherein the reinforcing sections (36,38) are made of a different material to that of the tyre (20). A method of prolonging the use of a tyre (20) of a roll wheel assembly (14) for a pulverizer (10) used for contacting and crushing a material, the method comprising: providing a reinforcing section (36) on an outer surface of the tyre (20) to provide an asymmetrical outside diameter outer surface on the tyre (20) at a location where the tyre (20) is subjected to wearing due to performing the crushing of the material; and providing a reinforcing section (38) on an inner surface (32) of the tyre (20) directly opposite the location where the tyre is subjected to wearing for minimizing localized thinning of the tyre. A method according to claim 6, wherein the reinforcing sections (36,38) are created by adding at areas on the tyre (20) where the tyre wearing is predictable. A method according to claim 6 or claim 7, wherein the thickness of the tyre (20) is increased by about 30% after providing the reinforcing sections (36,38) on the tyre. A method according to claim 8, wherein the weight of the tyre (20) is increased by not more than 10% after providing the reinforcing sections (36,38) on the tyre. A method according to any one of claims 6 to 9, wherein the reinforcing sections (36,38) are created by affixing additional material by means of weld deposition to an existing tyre (20). A method according to any one of claims 6 to 9, wherein the reinforcing sections (36,38) are created by casting them as part of the tyre (20) in an as-cast configuration. A method according to any one of claims 6 to 9, wherein the reinforcing sections (36,38) are preformed reinforcement sections placed in a casting mould prior to providing molten metal forming the balance of the tyre (20) so as to composite cast them into the tyre. A method according to any one of claims 6 to 9, wherein the reinforcing sections (36,38) are made as separate elements which are later mechanically affixed via fasteners or the like to an existing tyre (20). A method according to any one of claims 6 to 9, wherein the reinforcing sections (36,38) are created by sleeving them over and into an existing tyre (20).

Inventors: HAND BRYAN, MIZAK RONALD D, PIEPHO ROBERT R, HAND, BRYAN, MIZAK, RONALD D., PIEPHO, ROBERT R.
Applicants: BABCOCK & WILCOX CO, THE BABCOCK & WILCOX COMPANY
Application year: 1994
Main classification: B02C15
IPC codes: B02C15